Emission control at EDF Energy power station

The Promass 83F Coriolis flowmeter is a vital part of the molten sulphur control system used at the EDF Energy Cottam PS, to ensure electrostatic capture of all particulates in the waste gases

Controlling harmful emissions with the Promass 83F Coriolis flowmeter EDF Energy is one of the largest energy companies in the UK, distributing to over a quarter of the country's population.

The EDF Energy Cottam Power Station in Retford, Nottinghamshire, is a coal-fired power station with a production capacity capable of supplying up to 4% of the UK market.

Coal has been the mainstay of electricity generation in the UK for the past 50 years and still plays an important role, accounting for a third of the total UK generation.

The coal is finely ground before being mixed with warm air and burned in huge boilers.

The generated steam passes through a turbine making it rotate to generate electricity, which is then fed into the national grid.

Waste produced in the form of pulverised fuel ash is removed from the boiler gases by electrostatic precipitators before the gases pass up the chimneys.

In order to reduce harmful emissions, sulphur trioxide is injected into the precipitation inlet flow to change the resisitivity of the existing particles and enhance the performance of the electrostatic precipitators.

Too much sulphur trioxide will create a higher acid dewpoint and increased probability of cold-end corrosion and acid emission.

If there is too little, the electrostatic precipitator performance will suffer and release increased levels of particulate emissions to the atmosphere.

Measuring the flow of sulphur into the sulphur trioxide plant is therefore integral to this process, as is retaining the optimum temperature.

The sulphur flows at extremely high temperatures: the pipelines need to be trace-heated to maintain the fluid properties of the sulphur.

Promass 83F is more than up to the challenge with a process temperature capability of 350C, performing at pressures up to 350 bar.

In order for the application to work effectively, the sulphur has to remain in a liquid form, at above 135C, to prevent it from hardening, blocking the tubes and ultimately obstructing the process.

However, if the temperature exceeds 150C, the viscosity rises and the sulphur does not flow easily.

Maintaining the optimum temperature is therefore vital to achieving maximum effectiveness of the process.

Heating jackets were recommended as they can be placed over the Promass meter in order to maintain the optimum temperature for sulphur flow.

The process also demanded high accuracy at very low flow rates.

Due to the Promass 83F zero point accuracy, this was no problem.

What's more, in providing a short-tube Promass 83F, EDF Energy can clean the meter in the event of a problem.

This was of great benefit as the flowmeters previously in place had used bent tubes, preventing the maintenance staff from cleaning away build-up.

The short-tube design of the sensor is instrumental in keeping the plant operational and maintenance costs to a minimum as there is no longer the necessity to buy a replacement meter every time there is a problem.

The effect that this has had on the operation of the plant has been significant: the Promass 83F Coriolis flowmeter has improved performance and reduced maintenance costs.

The EDF Energy Electrical Control and Instrumentation Engineer, Paul Whitby, remarked: "The sensor design of Promass 83F does not block like other designs I have experienced, so the flow of liquid sulphur to the process is not interrupted.

The heating jackets are very well made and a perfect fit around the flowmeters, making heat transfer excellent! This system is so reliable that downtime has been virtually eliminated and emissions are also controlled as Promass 83F is part of the sulphur trioxide injection system.

I would be happy recommending the Promass 83F for other installations of a similar design to our own!".

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